1. Field of the Invention
The instant invention relates to an apparatus for production from oil wells. More particularly, the present invention relates to an apparatus that utilizes at least one injection pump, positioned in proximity to a subsea petroleum well, to provide hydraulic fluid for hydraulic pumping equipment positioned in the bottom of the well, in order to cause a flow of production oil.
2. State of the Art
The process of petroleum production includes the flow from a geological formation or reservoir, positioned at some hundreds or perhaps some thousands of meters below the surface, to installations positioned on the surface.
In the beginning of production from a reservoir the natural pressure normally is sufficient to establish the drainage of oil towards the surface. Thereafter, owing to the degree that the oil reserves of the reservoir are being exploited with the consequent diminution of pressure from the reservoir, it becomes necessary to employ a method for pumping the fluid from the well towards the surface, this operation is known as “an artificial lifting of petroleum.”
Some methods for lifting the petroleum from the well are known, for example, a pneumatic pump (also known in English as a “gas lift”), the use of bottom pumps, that maybe either of a centrifugal or reciprocating type.
The selection of the type of artificial petroleum lifting that will be utilized is done as a function of the characteristics of the well, its fluid and the available resources at the production site.
One of the available methods of lifting is the hydraulic jet pump (HJP) also known in English as “jet pumping”. In the present description, for the sake of simplification, this method will hereinafter be referred to simply as HJP.
The operational principle of the HJP is similar to that of ejectors, of the type usually found in processing plants. Basically, this system of production includes a tank for storage of hydraulic fluid, a hydraulic fluid injection pump, an ejector or injection pump and a separating vessel. Among these elements, only the ejector is located in the interior of the well.
The hydraulic fluid may be different from the produced oil and is pumped at high pressure toward the interior of the well by an injection pump. In the location in which the ejector is installed, in the bottom of the well, the hydraulic fluid is forced to flow through a restriction which includes an injection nozzle.
With this occurs a transformation of pressure energy to kinetic energy, in conformance to the first law of Thermodynamics. In the suction of the ejector, which is a point of low pressure, an entry of fluid, provided by the reservoir, occurs, owing [due] to the suction effects caused by the low pressure in the nozzle.
Soon thereafter, downstream of this point, there is a narrowing of the flow path, e.g. a throat, where an effective mixing of the hydraulic fluid and the fluid, provided from the reservoir, occurs. This results in the formation of a single fluid flow.
Thereafter, this fluid flow passes through a diffuser, where the area of flow increases gradually, which causes a transformation of the kinetic energy into energy of pressure, and with this the mixture of oil, provided from the formation, and the hydraulic fluid flow toward the surface.
The HJP has the following application advantages:
a) There are no moving parts in the interior of the well, which results in a device having great durability;
b) In certain configurations the bottom pump may be recovered by a reverse flow, thereby avoiding any necessity of an intervening operation in the well to substitute the pump;
c) An easy injection of chemical products, such as corrosion inhibitors is made possible;
d) In the case of a reservoir which produces heavy oil, one may utilize the hydraulic fluid to reduce the viscosity of the fluid produced by the reservoir either by diluting it, if a lighter oil is used as a hydraulic fluid, or by forming an inverse emulsion, if water is used as a hydraulic fluid;
e) It exhibits a good tolerance to sand and gas.
On the other hand, HJP presents some disadvantages which may be distinguished as follows:
A) Low energy efficiency which requires, a larger consumption of energy for its operation in comparison with other methods of artificial petroleum lifting. On the other hand, for petroleum wells, especially subsea wells, this factor is not relevant because in these situations the cost of energy is very low when compared with the other operational costs of the other methods of artificial petroleum lifting, such as the cost of intervention to repair or replace pumps positioned in the bottom of the well;
B) If the hydraulic fluid is water, it is necessary to undergo a separation process in the installations on the surface which may significantly overload the processing system;
C) Since an addition of liquid occurs in the region where the ejector is located, there is a diminution in the fraction of gas and consequently an increase in the apparent average specific mass inside the column of production. As a consequence of this the required discharge pressure of the pump also increases, making the whole system, i.e. the well, the injection pump, the Christmas tree and flowlines, operating at high pressure. This particular aspect represents a great limitation in the use of the HJP, in that high operational pressures require equipment that is much more robust, more expensive, and subject to major risks of accidents and leakage.
In review, an analysis of this method indicates that the major benefit of the HJP relates to its durability, the fact that there are no moving parts in the interior of the well. On the other hand, its limitation for application is, in many cases, the high pressure required for the injection of the hydraulic fluid.
In the case of the petroleum well being a subsea well, the situation is more serious in that usually the distance between the location of the platform, on which the injection pump is installed, and the subsea wellhead is much larger, generally more than a kilometer. In this case there would be the inconvenience of having to provide a hydraulic conduit, of a considerable length which would be able to support elevated pressures. This would increase the costs and the operational risks.
A method of hydraulic pumping by way of a piston (HPP) is also known in the art In this method an reciprocating double action piston pump is connected through an actuated piston axle to an reciprocating double action piston hydraulic motor. The motor and the pump are similar in their constructive aspects.
Hydraulic fluid is fed to this system to actuate an reciprocating ascending/descending of the piston of the motor. This motor piston is connected to the piston of the pump and as a consequence the latter also effects reciprocating movements that are ascending and descending.
When the piston pump affects a descending movement, at that same time there will occur a suction of the fluid to be pumped, into the superior chamber of the pump. There will be a discharge of fluid through the lower chamber.
When the pump piston effects an ascending movement, the situation will be inverted and the suctioned fluid will then to be discharged, initiating in this moment a new entry of fluid into the lower chamber.
As may be observed the instant process is a cyclical process.
The use of hydraulic turbines in petroleum wells for actuating a rotative hydraulic pump is also known. Examples of such a use include methods of using submerse centrifugal pumps (SCP) and progressive cavity pumps (PCP).
In a SCP a hydraulic turbine actuates an axial centrifugal pump; alternatively an assembly of these pumps may be connected in series. In a PCP a turbine actuates a screw pump. These two methods are well known in the art and will not be described herein in view of their being well known by those skilled in the art.
In conclusion, every pumping system that utilizes reciprocating pumps or rotative pumps to drain a petroleum reservoir from a production well either by means of the use of a hydraulic motor or by means of the use of a hydraulic turbine will always suffer limitations in its operation due to the elevated pressures of the hydraulic fluid injection system.
The present invention provides an apparatus that solves the problems mentioned above related to the high pressure injection of hydraulic fluid required by the bottomhole hydraulic pumping equipment, as will be seen in the following.